backend/tests: Add blackbox tests from Kotlin JVM

Added tests from testData/codegen/box directory. There are blackbox tests
in other directories and they are to be added.

backend.native/tests/external/codegen/blackbox/controlStructures/kt12908.kt

@@ -0,0 +1,20 @@
+var field: Int = 0
+
+fun next(): Int {
+    return ++field
+}
+
+
+fun box(): String {
+    val task: String
+
+    do {
+        if (next() % 2 == 0) {
+            task = "OK"
+            break
+        }
+    }
+    while (true)
+
+    return task
+}